Fluoride exposure changed the structure and the expressions of HSP related genes in testes of pubertal rats

Riboflavin Attenuates Fluoride-Induced Testicular Injury via Interleukin 17A-Mediated Classical Pyroptosis

Male reproductive toxicity of fluoride is of great concern worldwide, yet the underlying mechanism is unclear. Pyroptosis is a novel mode of inflammatory cell death, and riboflavin with anti-inflammatory properties has the potential to protect against fluoride damage. However, it is unknown whether pyroptosis is involved in fluoride-induced testicular injury and riboflavin intervention. Here, we first found that riboflavin could alleviate fluoride-caused lower sperm quality and damaged testicular morphology by reducing pyroptosis based on a model of ICR mice treated with NaF (100 mg/L) and/or riboflavin supplementation (40 mg/L) via drinking water for 13 weeks. And then, together with the results of in vitro Leydig cell modelsm it was confirmed that the pyroptosis occurs predominantly through classical NLRP3/Caspase-1/GSDMD pathway. Furthermore, our results reveal that interleukin-17A mediates the process of pyroptosis in testes induced by fluoride and riboflavin attenuation according to the results of our established models of riboflavin- and/or fluoride-treated IL-17A knockout mice. The results not only declare a new mechanism by which fluoride induces testicular injury via interleukin 17A-mediated classical pyroptosis but also provide evidence for the potential clinical application of riboflavin as an effective therapy for fluoride toxicity.

Exposure to Fluoride From in Utero to Puberty Alters Gonadal Structure and Steroid Hormone Expression in Offspring Rats

The reproductive toxicity of fluoride has been proven by a large number of studies. While the underlying mechanism of reproductive toxicity during pregnancy is still unclear. Hence, in this study, we investigated the effects of fluoride exposure on ovarian and testicular steroid hormone synthesis in young and adult rat offspring. We established a model of fluoride-exposed rat pups from in utero to puberty to explore the mechanisms of fluoride impacts on reproductive toxicity in the offspring. The results showed that NaF exposure did not affect the 3 weeks of age offspring. Whereas the body weight in both sexes significantly decreased, and the ovarian and testicular tissue structures were damaged at 11 weeks of age. In females, the total number of secondary follicles and mature follicles were significantly reduced after NaF exposure. Moreover, estradiol (E2) and follicle-stimulating hormone (FSH) levels in the females were significantly reduced in the 100 mg/L NaF exposure group. In males, the sperm viability and testosterone (T) were significantly decreased in the NaF exposure groups. Additionally, during steroidogenesis in ovaries and testes, fluoride remarkably decreased the expression levels of genes and proteins, including acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17a-hydroxylase (CYP17A1), and cholesterol side-chain cleavage enzyme (CYP11A1), while the mRNA levels of 17β-hydroxysteroid dehydrogenase (17β-HSD) decreased only in the testes. These results indicated that fluoride exposure disrupted the steroid hormone balance by changing several important steroidogenic-related genes associated with the development of the gonads, and damage the normal structure of the gonads in rat offspring.

Acrylamide-induced meiotic arrest of spermatocytes in adolescent mice by triggering excessive DNA strand breaks: Potential therapeutic effects of resveratrol

Background: Baked carbohydrate-rich foods are the main source of acrylamide (AA) in the general population and are widely consumed by teenagers. Considering the crucial development of the reproductive system during puberty, the health risks posed by AA in adolescent males have raised public concern.Methods: In this study, we exposed 3-week-old male pubertal mice to AA for 4 weeks to evaluate its effect on spermatogenesis using computer-assisted sperm analysis (CASA) and historical analysis. Flow cytometric analysis and meiocyte spreading assay were conducted to assess meiosis in mice. The expression of meiosis-related proteins and double-strand break (DSB) proteins were evaluated by immunoblot analyses. Additionally, isolated spermatocytes were used to explore the role of resveratrol in AA-induced damages of meiosis.Results: Our results showed that AA decreased the testicular and epididymal indexes, reduced sperm count and motility, and induced morphological disruption of the testes in pubertal mice. Subsequent meiotic analysis revealed that AA increased the proportion of 4C spermatocytes and decreased the proportion of 1C spermatids. The expression levels of meiosis-related proteins (SYCP3, Cyclin A1 and CDK2) were downregulated, and signaling proteins (γH2AX, p-CHK2 and p-ATM) expression levels were upregulated in AA-treated mice testes. Similar expression patterns were observed in primary spermatocytes treated with AA and these effects were reversed significantly by resveratrol.Conclusions: Our results indicate that AA induces meiotic arrest via persistent activation of DSBs, which may contribute to AA-compromised spermatogenesis. Resveratrol could serve as a potential therapeutic agent against AA-induced meiotic toxicity. These data highlight the importance of natural product supplementation for treating AA-related reproductive toxicity.

Alleviating effects of selenium on fluoride-induced testosterone synthesis disorder and reproduction toxicity in rats

Fluoride (F) exists widely in food, water and other natural resources, and can cause damage to the reproductive system of human and animals. Studies have shown that selenium (Se) is a necessary trace element to maintain the normal male reproductive system. However, it is not clear whether it can alleviate the damage of reproductive system induced by F. Hence, sodium fluoride (NaF) was administered singly in drinking water at 100 mg L^-1 alone and co-administered by drinking with sodium selenite (Na₂SeO₃) at 0.5, 1.0, 2.0 mg L^-1 for 10 consecutive weeks. The results demonstrated that the sperm deformity rate were increased significantly by F, however, it was improved significantly after the addition of 2.0 mg L^-1 Na₂SeO₃. The contents of glutathione peroxidase 4 (GPX-4), selenoprotein P (SePP), pregnenolone (PREG), androstenedione (ASD), and testosterone (T) were reduced obviously in the F group, however, it was increased significantly after adding 0.5, 1.0 and 2.0 mg L^-1 Na₂SeO₃. F decreased noticeably the mRNA and protein expression levels of steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side chain lyase (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17α-hydroxylase (P450c17) and 17β-hydroxysteroid dehydrogenase (17β-HSD), which was increased obviously after the addition of 1.0 and 2.0 mg L^-1 Na₂SeO₃. In summary, 2.0 mg L^-1 Na₂SeO₃ can alleviate testosterone synthesis disorder induced by F via reducing oxidative stress, increasing the level of selenoprotein in testis and regulating the content of related hormones and enzyme activity during testosterone synthesis pathway.

Challenges of fluoride pollution in environment: Mechanisms and pathological significance of toxicity - A review

Fluoride is an important trace element in the living body. A suitable amount of fluoride has a beneficial effect on the body, but disproportionate fluoride entering the body will affect various organs and systems, especially the liver, kidneys, nervous system, endocrine system, reproductive system, bone, and intestinal system. In recent years, with the rapid development of agriculture and industry, fluoride pollution has become one of the important factors of environmental pollution, and fluoride pollution in any form is becoming a serious problem. Although countries around the world have made great breakthroughs in controlling fluoride pollution, however fluorosis still exists. A large amount of fluoride accumulated in animals will not only produce the toxic effects, but it also causes cell damage and affect the normal physiological activities of the body. There is no systematic description of the damage mechanism of fluoride. Therefore, the study on the toxicity mechanism of fluoride is still in progress. This review summarizes the existing information of several molecular mechanisms of the fluoride toxicity comprehensively, aiming to clarify the toxic mechanism of fluoride on various body systems. We have also summerized the pathological changes of those organ systems after fluoride poisoning in order to provide some ideas and solutions to the reader for the prevention and control of modern fluoride pollution.

Interleukin 17A deficiency alleviates fluoride-induced testicular injury by inhibiting the immune response and apoptosis

The reproductive toxicity of fluoride (F) has been verified by various epidemiological and experimental studies. Our previous work suggested that the interleukin 17A (IL-17A) is involved in the testicular damage induced by excessive F exposure. In this study, we further investigated the role of IL-17A in F-induced testicular injury. Wild type (WT) and IL-17A knockout (IL-17A^-/-) mice were exposed to 0, 25, 50, or 100 mg/L sodium fluoride (NaF) for 90 days. We found that exposure to excessive F levels caused testicular damage, decreased semen quality, negatively affected testicular morphology, and increased the inflammatory response. Specifically, excessive F intake increased the expression levels of IL-17A in the testis and increased the protein levels of Act1, NF-κB, IL-17R, C/EBP-α, and TRAF6 in the IL-17A signaling pathway. The increase in IL-17A expression corresponded to increases expression of IL-17R, IL-6, IL-23, IL-1β, TGF-β and TNF-α as assessed by RT-PCR and ELISA assays. Remarkably, IL-17A knockout in mice ameliorated the effects of F on testicular damage, semen quality, testicular morphology, and the immune response. Additionally, we found the in vitro exposure of Leydig cells to NaF and recombinant IL-17A led to abnormal apoptosis and a decrease in testosterone secretion. Our findings prove that IL-17A plays a key role in the exacerbation of testicular injuries in F-exposed mice, and that IL-17A deficiency can alleviate F-induced injury by inhibiting the immune response and apoptosis in the testis. These data suggest that targeting IL-17A may be a useful therapeutic strategy for treating F-mediated toxicity in the testis.

Exposure of Fluoride with Streptozotocin-Induced Diabetes Aggravates Testicular Damage and Spermatozoa Parameters in Mice

Diabetes mellitus is the most common chronic disease worldwide that causes numerous complications, including male infertility. The prevalence of DM is 451 million people and estimated that would increase to 693 million in 2045. Fluorosis caused by drinking water contaminated with inorganic fluoride is a public health problem in many areas around the world. Previous studies have shown that fluoride exposure damages the male reproductive function. This study aimed to evaluate the fluoride sub-chronic exposure on the spermatozoa function in streptozotocin (STZ)-induced diabetic mice. After confirming diabetes by measuring blood glucose levels, the male mice received 45.2 ppm of fluoride added or deionized water. We evaluated several parameters in diabetic mice exposed to fluoride: standard quality analysis, the mitochondrial transmembrane potential (ψm), the caspase activity in spermatozoa, urinary fluoride excretion, and histological evaluation in the testes. After 60 days of fluoride-exposure, diabetic mice, significantly decreased sperm quality (motility, viability, and concentration). Spermatozoa from fluoride-exposure in diabetic mice presented a significant decrease in ψm and a significant increase in activity caspase 3/7. Urinary fluoride excretion was decreased in diabetic mice exposed to fluoride. Subchronic fluoride exposure of mice with STZ-induced diabetes aggravated testicular damage and the spermatozoa function.

Fluoride-induced unrestored arrest during haploid period of spermatogenesis via the regulation of DDX25 in rats

The effect of fluoride as an ongoing topic has attracted much attentions due to the decline in overall human fertility worldwide. However, whether fluorine causes a temporary stimulus or permanent damage to the male reproductive system, as well as the mechanism of fluoride influencing spermatogenesis remained unclear. 48 adult male rats were randomly divided into four groups (twelve each). Control group received the distilled water, while the other three groups were treated with 25, 50, 100 mg/L NaF via drinking water for 8 weeks. Six rats from each group were selected randomly to detect the levels of various indices related to spermatogenesis. The remaining rats were given only distilled water and left for recovery of a period of 2 weeks. Results showed that the levels of serum CK, ALP, CHE, BUN, UA, and Cr, testis morphology and the ultrastructure of sperm acrosome and chromatoid body (CB) were significantly changed by fluoride. Interestingly, the elongated spermatid counts, spermatids elongation ratio, and mRNA expressions of Prm1/2 and MIWI, TDRD1, TDRD 6, TDRD7, PABP, and Hsp72 related to CB decreased markedly in fluoride treatment groups compared to the control. Furthermore, the expression levels of DDX25 and associated regulatory proteins like CRM1, HMG2, H4, TP2, and PGK2 were down-regulated by fluoride. After 2-weeks withdrawal period, out of the 19 altered spermatogenesis indicators, 15 indicators in 100 mg/L group and 3 indicators in 50 mg/L group still exhibited a significant change, while none showed change in 25 mg/L group. These results proved that the reversibility of fluoride toxicity is dose-dependent on the male reproductive system. Meanwhile, fluoride caused unrestored arrest during the haploid period of spermatogenesis, where reduced DDX25 and associated regulatory proteins play a crucial role in this process, which could provide the underlying insights to the toxic mechanism of fluoride induced male reproductive toxicity.

The effects of high-fructose corn syrup consumption on testis physiopathology-The ameliorative role of melatonin

This study investigated the ameliorative role of melatonin (MLT) and the effects of a long-term intake of high-fructose corn syrup (HFCS) on the male reproductive system. Thirty-six male Sprague Dawley rats were randomly divided into 3 groups as follows: Control, HFCS and HFCS + MLT. Testis and epididymal weights were measured. Malondialdehyde (MDA) levels, superoxide dismutase (SOD) and catalase (CAT) activities, total testosterone levels, testicular histopathological damage scores were evaluated, and immunohistochemical analyses were performed on testicular tissue. Epididymal weights were significantly lower in the HFCS + MLT group than those of the control and HFCS groups. MDA was significantly increased, while SOD and CAT activities were reduced in the HFCS group compared with the control group. Administration of melatonin significantly increased SOD and CAT activities in the HFCS + MLT group. Histopathological evaluation revealed slight hyperaemia and oedema in the stromal tissue of rat testes in the HFCS group. Sperm count and Johnsen's testicular biopsy score (JTBS) were significantly decreased in the HFCS group. Immunohistochemical analysis revealed that HSP, iNOS, MDA, OPN and VEGF values were significantly increased in the HFCS group. However, melatonin ameliorated the immunohistochemical scoring. Our results showed that a long-term intake of HFCS caused testicular damage. Melatonin may be a promising pharmacological agent against testicular toxicity induced by HFCS.

The Contribution of Fluoride to the Pathogenesis of Eye Diseases: Molecular Mechanisms and Implications for Public Health

This study provides diverse lines of evidence demonstrating that fluoride (F) exposure contributes to degenerative eye diseases by stimulating or inhibiting biological pathways associated with the pathogenesis of cataract, age-related macular degeneration and glaucoma. As elucidated in this study, F exerts this effect by inhibiting enolase, τ-crystallin, Hsp40, Na⁺, K⁺-ATPase, Nrf2, γ -GCS, HO-1 Bcl-2, FoxO1, SOD, PON-1 and glutathione activity, and upregulating NF-κB, IL-6, AGEs, HsP27 and Hsp70 expression. Moreover, F exposure leads to enhanced oxidative stress and impaired antioxidant activity. Based on the evidence presented in this study, it can be concluded that F exposure may be added to the list of identifiable risk factors associated with pathogenesis of degenerative eye diseases. The broader impact of these findings suggests that reducing F intake may lead to an overall reduction in the modifiable risk factors associated with degenerative eye diseases. Further studies are required to examine this association and determine differences in prevalence rates amongst fluoridated and non-fluoridated communities, taking into consideration other dietary sources of F such as tea. Finally, the findings of this study elucidate molecular pathways associated with F exposure that may suggest a possible association between F exposure and other inflammatory diseases. Further studies are also warranted to examine these associations.

Positive PCNA and Ki-67 Expression in the Testis Correlates with Spermatogenesis Dysfunction in Fluoride-Treated Rats

The present study aimed to evaluate the effect of fluoride (F) on spermatogenesis in male rats. F^- at 50 and 100 mg/L was administered for 70 days, after which the testicular and epididymis tissues were collected to observe the histopathological structure under a light microscope. The ultrastructure of the testis and sperm was also examined via transmission electron microscopy. The apoptosis of spermatogenic cells was measured through terminal deoxynucleotidyl transferase dUTP nick end labeling staining. The expression of proliferation factors, namely, proliferating cell nuclear antigen (PCNA) and Ki-67, in the testicular and epididymis tissues, were assayed through immunohistochemistry. F^- at 50 and 100 mg/L significantly damaged the structure of the testis and epididymis, and the testis and sperm ultrastructure exhibited various changes, including mitochondrial swelling and vacuolization, and apsilated and raised sperm membrane. F treatment significantly increased spermatogenic cell apoptosis in the testis. PCNA (P < 0.01) and Ki-67 (P < 0.01) also presented positive expression in the testis. By comparison, no significant changes occurred in the epididymis. In summary, excessive F intake results in spermatogenesis dysfunction by damaging the testicular structure and inducing spermatogenic cell apoptosis in male rats. The positive expression level of PCNA and Ki-67 was a good response to spermatogenesis dysfunction.

Effects of Fluoride and/or Sulfur Dioxide on Morphology and DNA Integrity in Rats' Hepatic Tissue

This study was aimed to evaluate the toxic effects of fluoride (F) and/or sulfur dioxide (SO₂) on morphology and DNA integrity in liver of male rats. For this, 96 Wistar rats (12-week-old) were randomly divided into four groups after 1-week adaptive breeding: the control group, treated with deionized water; the NaF group, administered high F (100 mg NaF/L in the drinking water); the SO₂ group, with sulfur dioxide in ambient air (15 ppm SO₂, 4 h/day); and NaF + SO₂ group, treated with high F and sulfur dioxide together for 8 consecutive weeks. The body weight, liver organ coefficient, morphology, and DNA damage in the liver of rats were examined. The results showed that the body weight and liver organ coefficient were not significantly changed; however, significant pathological changes of liver tissues were observed in the NaF + SO₂ group compared with the individual treated groups and control group. Furthermore, comet assay indicated that DNA damage in liver was significantly increased in the F and/or SO₂ treatment groups at 2, 4, 6, and 8 weeks, especially at 4 weeks. These results indicate that the liver morphology and DNA integrity of rats are adversely affected by F and/or SO₂ exposure.